1. Technical Field
The present disclosure relates to a reflection type liquid crystal device (LCD) and a projector.
2. Related Art
In recent years, the contrast of liquid crystal projectors has been improved, and the VA (vertical alignment) liquid crystal material has increasingly replaced the TN (twisted nematic) liquid crystal material. The VA liquid crystal material has a high contrast in the direction perpendicular to the LCD panel and, in addition, can obtain a large viewing angle by simple viewing angle compensation. When the viewing angle becomes large in a projector, the contrast in the angle range taken into the projection lens improves, thereby increasing the contrast of projected images.
The VA liquid crystal material for use in a liquid crystal television and the like is usually structured to obtain a high contrast in a wide viewing angle range by combining an optical compensation plate (a so-called C plate). In contrast, such viewing angle compensation cannot be achieved in a VA liquid crystal panel for use in a liquid crystal projector. This is because the light bulb has extremely high definition, and thus an orientation controller (a projection or an electrode opening) adopted in a liquid crystal television cannot be built in a minute pixel, which inevitably results in that the orientation is controlled by tilting (pretilt) the VA liquid crystal at several angles from the vertical state. Even when the VA liquid crystal having such a pretilt is tried to compensate by the C plate, a phase difference remains in the direction perpendicular to the liquid crystal panel, and thus high contrast cannot be obtained.
Japanese Unexamined Patent Application Publication No. 2008-164754 discloses a technique in which the C plate and an optical compensation plate (a so-called O plate) having an optical axis which tilts with respect to the element surface are combined, and the viewing angle characteristics are compensated for by disposing the C and O plate combination on the external surface of the liquid crystal panel, so that high contrast and wide viewing angle characteristics are obtained. Moreover, Japanese Unexamined Patent Application Publication No. 2009-37025 discloses a technique in which the C plate is disposed in a tilted state on the outside of a transmission type VA liquid crystal panel so that the optical axis of the liquid crystal panel and the optical axis of the C plate are parallel to each other, and the front phase difference of the VA liquid crystal is compensated for only with the C plate.
It is also considered that the above-described optical compensation plate is adapted to a reflection type VA liquid crystal panel. However, when the technique of Japanese Unexamined Patent Application Publication No. 2008-164754 is employed, two expensive optical compensation plates are required, resulting in a cost increase. According to the technique of Japanese Unexamined Patent Application Publication No. 2009-37025, there is a possibility that the C plate is adhered to the liquid crystal panel in a state where the tilt direction of the C plate shifts due to the attachment error or the like caused by an attachment jig. Moreover, there is also a possibility that the C plate is formed with a shift between the plate surface and the optical axis due to an error in manufacturing the C plate. Furthermore, there is also a possibility that the azimuth angle of the liquid crystal orientation shifts in the VA liquid crystal panel.
When variations in the optical conditions, such as the shift in the tilt direction or the shift in the liquid crystal orientation, occur, high contrast is difficult to obtain in some cases even when the C plate is disposed in a tilted state on the external surface of a reflection type VA liquid crystal panel so that the optical axis of liquid crystal molecules and the optical axis of the C plate are parallel to each other.